1. Field of the Invention
The present invention relates to an absorbent article that uses nonwoven fabric.
2. Related Art
Conventionally, nonwoven fabrics are used in a wide range of fields from hygienic products such as baby diapers or feminine care articles (sanitary napkins) to cleaning products, such as wipers, or medical products, such as masks. Such nonwoven fabrics are used in many different fields, but when actually used in products of each of those fields, it is necessary that the nonwoven fabrics are manufactured with the properties and structures appropriate for their intended use.
Nonwoven fabric is fabricated by forming a fibrous layer (web) using a dry method or a wet method, and then bonding the fibers in a fibrous layer together using a chemical bonding method or a thermal bonding method. In processes that bond the fibers to compose the fibrous layer, there is a method in which a plurality of needles are repeatedly inserted into the fibrous layer, and a method in which physical force, such as a blowing race, is externally applied to the fibrous layer.
These methods however, only entangle the fibers and do not adjust the orientation or the arrangement of the fibers in the fibrous layer, or the shape of the fibrous layer. In other words, the fiber beds manufactured using these methods were simply sheet-shaped nonwoven fabrics.
Also, if a predetermined liquid of excreta is brought into contact with a nonwoven fabric used in a cover sheet, and the like, of an absorbent material, for example, a nonwoven fabric having an uneven surface is preferred in order to maintain or improve the feeling against the skin. (e.g. see Japanese Patent No. 3587831, hereinafter referred to as Patent Document 1)
The following information is disclosed in Patent Document 1. A plurality of fibrous layers, a first fibrous layer of a top layer, and a second fibrous layer of a bottom layer, composed of fabrics having different heat contraction characteristics are partially heat-bonded in predetermined patterns. The first fibrous layer partially bulges due to the heat contraction of the second fibrous layer.
When nonwoven fabrics, such as those described in Patent Document 1, are used as a surface sheet (top sheet) in a skin contact surface of an absorbent article, the following problems exist in the absorbent article relating to liquid infiltration performance and liquid return suppression performance.
An upper, first fibrous layer and a lower, second fibrous layer are heat-bonded in a predetermined pattern. The heat-bonded portion becomes a concave shape, and is substantially turned to film. An area occupancy rate of the heat-bonded portion is 11.5%. Menstrual blood that has migrated into the concave portion, that is the heat-bonded portion, becomes trapped there, and gradually travels into the top sheet from the adjacent non-heat-bonded portions. Therefore, when menstrual blood builds up in the concave portions, and if the wearer undergoes a change in their activity, there is the possibility that that menstrual blood will leak to the first fibrous layer surface of the surrounding the concave portions. Therefore, there is room to improve liquid infiltration performance.
The upper, first fibrous layer is partially bulged due to the heat contraction of the lower, second fibrous layer. The second fibrous layer is configured by a heat-contraction fiber with a high heat contraction rate, as such it coils due to heat-contraction. Therefore, the second fibrous layer heat-contracts and catches the surrounding fibers, so the second fibrous layer is in a state where there is a highly dense collection of fibers. This causes a highly dense region in the second fibrous layer to be formed at the backside of the top sheet. When this happens, menstrual blood, which should be absorbed, has difficulty in moving from the high-density region to an absorbent just below, and readily builds up in the high-density region. In other words, repeatedly excreted menstrual blood builds up in high-density regions of the backside of the top sheet, and takes an extremely long time to travel to the lower absorbent layer. Therefore, when the menstrual blood builds up at the backside of the top sheet, there is the possibility that the menstrual blood can leak to the first fiber layer surface if the wearer undergoes a changes in their activity. Therefore, there is room to improve liquid return suppression performance.
In this way, there is demand for an absorbent article with more comfortable performance, in which nonwoven fibers having concave portions and convex portion are used as a surface sheet (top sheet), which comes into contact with the skin. Particularly, this can help alleviate the problem of soiling the skin and causing the wearer to have a sticky feeling if menstrual blood is repeatedly excreted, or pressure is applied to contact the skin, such as in a sitting posture, and to improve liquid infiltration performance and liquid return suppression performance.